Photography – Camera shake sensing – Having stabilization system
Utility Patent
1998-12-30
2001-01-02
Perkey, W. B. (Department: 2851)
Photography
Camera shake sensing
Having stabilization system
C396S079000, C359S557000, C359S689000, C359S823000
Utility Patent
active
06169853
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a zooming optical system that has an image-vibration compensation function, and is applicable to cameras such as cameras using a photographing film, still or video cameras, and the like.
Conventionally, cameras provided with an image-vibration compensation system for compensating vibration of image due to the hand-held shake applied to the camera has been known.
An example of the image-vibration compensation system for camera is described in Japanese Patent Provisional Publication HEI 6-265827.
In the conventional image-vibration compensation system disclosed in the above publication, a compensation lens is decentered (i.e., moved in a plane which is perpendicular to the optical axis of the photographing lens) to compensate trembling of the image caused by the hand-held vibration applied to the camera. Specifically, in the publication above, a zooming optical system for a camera is disclosed, and the zooming optical system includes an image-vibration compensation lens. The image-vibration compensation lens as disclosed has, however, a relatively strong refractive power, and therefore, various types of aberrations which may affect image quality would cause when the compensation lens is decentered for compensation. In order to cancel such aberrations, further lenses should be provided. Thus, the number of lenses included in the compensation lens system increases. Due to relatively large number of lenses, the weight of the compensation lens system increases, and accordingly a quick movement of the compensation lens is prevented. Since the compensation lens has a strong power, the compensation can be done by relatively small movement, theoretically. Practically, however, the compensation lens should be driven at high accuracy. To drive a relatively heavy lens system at high accuracy is difficult, and therefore, it is difficult to obtain sufficient compensation result in such a system.
Furthermore, according to the publication, focusing is done by moving (1) a lens group closest to an image plane, (2) an entire lens group including an aperture, or (3) a lens group including the aperture and a lens group for image-vibration compensation.
In a recently employed zoom lens for a still camera or video camera, a back focus is very short when the focal length of the zoom lens is shortest. Thus, the lens group closest to the image plane is required to have a relatively large diameter. Therefore, such a lens group that is arranged on the image plane side may be too heavy to move for focusing.
Lenses arranged close to the aperture member are relatively small. However, recent zoom lenses are required to have a relatively large ratio of a variable power, and accordingly, the number of lenses included in a lens group which has the aperture member is relatively large. Therefore, such a lens group may be too heavy to move for focusing.
If the lens group which includes the image-vibration compensation lens is moved also for focusing, required is a mechanism for moving the image-vibration compensation lens either in a direction parallel to the optical axis or in a direction perpendicular to the optical axis. Such a mechanism would be very complicated.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a zooming optical system having an image-vibration compensation system, in which a lens group for image-vibration compensation can be moved quickly with a relatively simple structure, and does not make the zooming and focusing mechanisms complicated.
For the above object, according to the invention, there is provided a zooming optical system, which is provided with a plurality of lens groups that are moved to change a focal length of the zooming optical system. Each of these lens groups is driven to move unitarily for zooming. One of the plurality of lens groups, which includes an aperture member, has a focusing lens group that is driven to move for focusing, and an image-vibration compensation lens group that is driven to move for compensating trembling of image due to a hand-held shake applied to the zooming optical system.
Since part (i.e., the focusing lens group) of the lens group, which has the aperture member, is constituted to move for focusing, and another part (i.e., the image-vibration compensation lens group) of the lens group is constituted to move for the image-vibration compensation, each of the lenses moved for focusing and image-vibration compensation can be formed relatively light in weight, and accordingly, can be driven quickly and accurately. Further, driving mechanisms for focusing and image-vibration compensation can be simplified.
Optionally, the aperture member is arranged between the focusing lens group and the image-vibration compensation lens group.
This structure also simplifies the constitution of the driving mechanisms for focusing and image-vibration compensation.
It is preferable that another lens group is arranged on an object side of the lens group which includes the aperture member and the focusing and image-vibration compensation lens groups. With this structure, the driving mechanisms for the focusing and image-vibration compensation lens groups can be arranged at midst portion of all the lens groups included in the zooming optical system. Such an arrangement may prevent interference of the driving mechanisms with respect to the other structural members.
In particular, a decentering amount of the image-vibration compensation lens group DEC is defined by equation (1):
DEC≈(f
1a
•f
1b
•tan&egr;)/(f
1a
−f
1b
) (1)
where,
DEC denotes an amount, in the direction perpendicular to the optical axis OX of movement of the image-vibration compensation lens group,
f
1a
denotes a composite focal length of lens groups located on an object side of the image-vibration compensation lens group (the image-vibration compensation lens group excluded),
f
1b
is a composite focal length of the lens groups located on the object side of the image-vibration compensation lens group and the image-vibration compensation lens group, and
&egr; is an angle by which the optical axis OX is rotated with respect to a point where the optical axis OX intersects an object side surface of a lens which is closest to the object (see FIGS.
2
A,
2
B,
7
A and
7
B).
It is preferable that the zooming optical system satisfies condition (2):
0.15<s
min
/y<0.5 (2)
where, s
min
denotes a minimum value of equivalent air distance s between a lens surface or an aperture plane which is located on the object side of the image-vibration compensation lens group and is closest to the image-vibration compensation lens group, and a lens surface or an aperture plane which is located on the image side of the image-vibration compensation lens group and is closest to the image-vibration compensation lens group, and y denotes the largest image height of the zooming optical system.
It is further preferable that the hand-vibration compensation lens group includes at least a pair of cemented positive and negative lenses, and condition (3) is satisfied:
20<&ngr;p−&ngr;n (3)
where, &ngr;p represents an average of Abbe numbers of positive lenses which are included in the cemented lens; and
&ngr;n represents an average of Abbe numbers of negative lenses which are included in the cemented lens.
Further optionally, the image-vibration compensation lens group includes at least one aspherical surface. By forming the aspherical surface, aberrations can be compensated easily.
Furthermore, it is preferable that condition (4) is satisfied:
1.0<ft/f3<2.0 (4)
where, ft is a focal length of the zooming optical system when located at a TELE extremity; and
f3 is a focal length of the image-vibration compensation lens group.
Still further, it is preferable that condition (5) is satisfied:
0.09<L3/y<0.25 (5)
where, L3 is an equivalent air distance between a surface, of the image-vibration compensation lens group, located closest to the object and a surface,
Hasushita Sachio
Ito Takayuki
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
Perkey W. B.
LandOfFree
Zooming optical system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Zooming optical system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Zooming optical system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2490688